Electron discharge device having at least one electrode mounted by a meander-type insulator



June 10, 1969 R c, KREUCHEN ET AL 3,449,617 ELECTRON DISCHARGE DEVICEHAVING AT LEAST our; ELECTRODE MOUNTED BY A MEANDER-TYPE INSULATOR Filedon. 24, 1966 Sheet 3,449,61 7 CTRODE June 1969 K. H. R. c. KREUCHENETAI- ELECTRON DISCHARGE DEVICE HAVING AT LEAST ONE ELIE MOUNTED BY AMEANDER-TYPE INSULATQR Sheet Filed Oct. 24, 1966 FIGZ FIG. 3

United States Patent US. Cl. 315-5.34 8 Claims ABSTRACT OF THEDISCLOSURE An electron discharge device, such as a klystron comprisesmeans for producing electrons, electrostatic focussing means forconstraining said electrons to travel as a beam past energy interchangemeans, and means for collecting said electrons. The focussing meansincludes one electrode having a central aperture for the beam locatedclosely adjacent to a conducting surface of said energy interchangemeans. The said electrode is mounted by means of an insulator whichcontacts said electrode and said conducting surface and is formed as ameander so that there is no direct path on the surface of said insulatorfrom a point of contact with said electrode to a point of contact withsaid conducting surface.

This invention relates to electron discharge devices and it relatesespecially although not exclusively to klystrons.

In a klystron, the electrons from the cathode are focussed to form abeam which passes through successive cavities before being collected bya collecting electrode. The focussing means have usually beenelectromagnetic, but such means render the klystron heavy and bulky, andit has therefore been proposed to substitute electrostatic focussing forelectromagnetic focussing. This proposal has however encounteredproblems of insulation having regard to the high potential differencesrequired between electrodes to achieve electrostatic focussing. Theinsulation problem is for example encountered in mounting focussingelectrodes accurately in position close to but insulated from the wallsof the cavities, a large potential difference being required between thefocussing electrode and the cavity wall.

It has been found that conducting particles are liable to be depositedon the surface of insulators. within the envelope of the klystroncausing leakage across the insulators, such deposition occurringespecially during the degasing baking operation which is a final stagein the manufacture of the tube.

Similar problems may be encountered in other electron discharge deviceswhich incorporate electrostatic focussing means for constrainingelectrons to travel as a beam past energy interchange means, and theobject of the invention is to reduce the problem of insulationencountered in such a device.

According to the present invention there is provided an electrondischarge device comprising means for producing electrons, focussingmeans for constraining said electrons to travel as a beam, and means forcollecting said electrons, and wherein said focussing means includes atleast one electrode having a central aperture for the beam, a conductingsurface adjacent said electrode, which may be a surface of said energyinterchange means, said electrode being mounted by means of an insulatorwhich contacts said electrode and said conducting surface and is formedas a meander so that there is no direct path on the surface of saidinsulator from a point of contact with said electrode to a point ofcontact with said conducting surface.

In order that the present invention may be clearly understood andreadily carried into etfect it will now be described with reference tothe accompanying drawings of which:

FIGURE 1 illustrates a longitudinal sectional view of a klystronaccording to one example of the invention,

FIGURE 2. is a sectional view taken on the line II of FIGURE 1, and

FIGURE 3 is a perspective view of a focussing electrode of the klystron.

Referring to FIGURE 1, the klystron which is illustrated comprises anelectron gun 1 including a thermionic cathode, four resonant cavities 2,3, 4 and 5 and a collector electrode 6, arranged in that order along theaxis of the klystron. The electron gun may be of any suitableconstruction but it is preferably of the construction described andclaimed in co-pending United States application Ser. No. 588,777 filedOct. 24, 1966 by Karl Heinz Robert Christian Kreuchen one of theapplicants of the present application. Each of the cavities is formed bytwo transverse copper walls and by part of the copper envelope of theklystron, the transverse walls being denoted by the references 7 and 8in the case of each cavity and the copper envelope or the klystron beingdenoted by the reference 9. The walls 7 and 8 are formed with drifttubes 10 and 11 in known manner, having central apertures which areco-axial. All the cavities have plungers 12 which can be moved radiallywithin the cavities for the purpose of tuning. The cavity 2 is the inputcavity and high frequency signals can be fed to this cavity by way of acoupling loop 13. The cavity 5, on the other hand, is the output cavityand is coupled to an output waveguide 14 through a dielectric window 15.

To enable the electrons from the source 1 to be focussed so as to form aconcentrated axial beam which passes through the cavities 2, 3, 4 and 5-and is finally collected by the collector electrode 6, electrostaticfocussing electrodes 16, 17 and 18 are provided between each pair ofcavities. When the klystron is operational, a high potential ismaintained on the electrodes 16, 17 and 18 relative to the walls 7 and 8of the cavities and to the envelope 9', and the electrodes 16, 17 and 18co-act with the apertured walls 7 and 8 to form converging electrostaticlenses. Each of the electrodes 16, 17 and 18- is at a fixed distancefrom the respective walls 7 and 8 of the two adjacent cavities, and themounting is achieved, in the case of each focussing electrode, by meansof a ceramic insulator 19. Each focussing electrode and insulator is ofthe same construction, and the following description of the electrode 17and its respective insulator is therefore applicable to all. As can beseen especially from FIGURE 3, the electrode 17 is in the form of aplanar member having a central aperture for passage of the beams. Lips21 and 22 of the electrode 17 at four angularly spaced positions, allthe lips 21 being shown by dotted lines in FIGURE 2. The lips 21 and 22thus form four arcuate grooves, equiangularly spaced round thecircumference of the electrode 17, the angular extent of each groovebeing less than 45 The insulator 19 has a central aperture, in whichthere are four equi-angularly spaced tongues 23 complementary to thefour grooves formed by the lips 21 and 22. The size of the electrode 17relative to the aperture in the insulator 19* is such that the electrodecan be inserted in an axial direction into the aperture with thecircumferential grooves located between the tongues 23, whereupon theare provided on both edges electrode can be rotated by approximately 90to cause v the tongue to enter the grooves, restraining the electrodefrom axial movement. The electrode 17 is located in the aperture of theinsulator 19 so that a tapped radial hole 51 in the electrode is alignedwith a radial hole 52 in the insulator 19. The lead passes through thehole 52 and an aligned hole 53' in the metal envelope 9 and terminatesin an end cap 54. Between the insulator 19 and the end cap 54, the leadis sheathed by a ceramic sleeve 55, which has an end portion 56 ofreduced diameter projecting into the hole 52 in the insulator 19. Toinsulate the end cap 54 from the metal envelope 9, it is secured to oneend of a stand-off insulator 57, the other end of which is secured to aflanged metal piece 58- welded to another flanged metal piece 59, theinner end of which is in turn welded to the envelope 9 around the edgeof the hole 53. The end cap 54 and the flanged metal piece 58 are eachsecured to the insulator 57 by a multi-step brazing process such asdescribed in British patent specification No. 891,705.

The insulator 57 is of a fluted cylindrical form, formed on its internalsurface with three annular grooves, being as can be seen in FIGURE 2,re-entrant towards the envelope 9. It has been found that thisconstruction of in-- sulator reduces the risk of conducting particlesbeing deposited over the inner surface of the insulator 57 in such a wayas to cause electrical leakage from the envelope 9 to the end cap 54.

The mounting insulator 19 for the electrode 17 is a one piece memberformed of high grade ceramic and the apertured central part thereof hasthree limbs 33 each in the form of a zig-zag or meander. The outer endof each limb is enlarged to form a foot 34 which, as can :be seen inFIGURE 1, is thicker, measured in the axial direction, than the rest ofthe insulator 19. Both the circumferential and axially facing surfacesof the feet 34 are accurately ground, after the ceramic insulator hasbeen fired, in relation to the central aperture of the insulator 19 andthe tongues 23, and the axial facing surfaces of the feet 34 contactwalls 7 and 8 of the adjacent cavities, whilst the circumferentialsurfaces of the feet contact the inner surface of the envelope 9. Inthis way, the location of the electrode is accurately determined.Moreover, as will be appreciated from a consideration of FIGURES 1 and2, there is no direct path on the surface of the insulator 19 from theelectrode 17 to either of the adjacent walls 7 and 8, or the envelope9-. Any path on the surface of the insulator 19 is long compared withthe shortest distance from a point of contact with the electrode and apoint of contact with the conductive surfaces 7, 8 and 9. This featureserves to reduce the risk of the klystron being rendered inoperative byreason of the surface of the insulator becoming conductive. Othermeander forms for the insulator 17 could produce a similar result to thezigzag meander illustrated.

Although the invention has been described herein as applied to aklystron, it is also applicable to other high power tubes such astra'velling wave tubes.

What we claim is:

1. An electron discharge device comprising means for producingelectrons, focussing means for constraining said electrons to travel asa beam past energy interchange means, and means for collecting saidelectrons, and wherein said focussing means includes at least oneelectrode having a central aperture for the beam a conducting surfaceadjacent said electrode, said electrode :being mounted by means of aninsulator which contacts said electrode and said conducting surface, andis formed as a meander so that there is no direct path on the surface ofsaid insulator from a point of contact with said electrode to a point ofcontact with said conducting surface.

2. A device according to claim 1 in which said electrode and saidinsulator are coplanar and said insulator comprises a plurality of limbseach formed as a zig-zag.

3. A device according to claim 1 and said adjacent conducting surfacebeing a part of said energy interchange means.

4. A device according to claim 3 in which said electrode and saidinsulator are co-planar and said insulator comprises a plurality oflimbs each formed as a zig-zag, and the outer end of each of said limbsis formed with a foot having a circumferential surface engaging theinner circumferential surface of a conducting part of the envelope ofsaid device and having at least one axially facing surface engaging saidconducting surface of said energy interchange means.

5. A device according to claim 4 in which the foot on each of said limbshas oppositely facing axial surfaces engaging conducting surfaces of twosuccessive energy interchange means, the arrangement being'such thatsaid focussing electrode is held by said insulator spaced from both saidenergy interchange means.

6. A device according to claim 1 in which said insulator has a centralaperture in which said electrode is secured, said electrode and saidinsulator being formed with interengaging parts such that the electrodecan be withdrawn from the central aperture following a rotation of saidelectrode.

7. A device according to claim 6 in which said electrode when secured inposition is held against rotation in said central aperture by a leadwhich is connected to the electrode and passes through the insulator.

8. A device according to claim 1 in which said insulator comprises a onepiece ceramic member.

References Cited UNITED STATES PATENTS 8/1960 Albert 313-254 X 5/1961Vaccaro et al. 3155.34

US. Cl. X.R.. 313-254; 3153.5

